Use of injectable progesterone at the beginning of the TAI protocol is not necessary in super-early resynchronization started 14 days after artificial insemination in Bos indicus beef heifers.

In a protocol for the resynchronization of ovulation starting 14 days (D14) after timed artificial insemination, the effects of short-action injectable progesterone (P4i) administration and the length of treatment with an intravaginal progesterone (P4) device on follicular dynamics, the conception rate (P/AI) and the percentage of false positives were evaluated in 1065 Nelore heifers previously timed-inseminated. On D14, P4 devices were inserted, and heifers allocated, based on a 2 × 2 factorial design, to receive (P4i) or not 50 mg of P4i (NoP4i), and to remove the P4 device after 6 (6Day) or 8 days (8Day). At the time of P4 device removal (D20 and D22), non-pregnancy diagnosis was performed using vascularization of the corpus luteum (VCL) evaluated. At this time, non-pregnant heifers received 150 µg of D-cloprostenol, 0.6 mg of estradiol cypionate and 300IU of eCG. TAI was performed 48 h after P4 device removal. For these heifers, ultrasound examinations were performed at P4 device removal and at TAI to evaluate follicular dynamics and at 30 days after TAI to evaluate the P/AI. Pregnant heifers based on VCL were evaluated using B-mode ultrasonography 10 days after Doppler ultrasound to evaluate the percentage of false positives. Statistical analyses were performed using the GLIMMIX procedure of SAS. There were no interaction effects between P4i and duration of treatment with a P4 device. The P/AI was diagnosed by Doppler, 1st TAI, 2nd TAI, total and percentage of false positives did not differ between heifers receiving or not P4i. Similarly, duration of treatment with a P4 device did not influence the P/AI by Doppler, 1st TAI, 2nd TAI and total. However, the percentage of false positives diagnoses was higher in 6Day heifers (P = 0.01). The diameter of largest follicle at P4 device removal was greater in the 8Day heifers (P = 0.001), and at TAI was higher in the P4i-treated heifers (P = 0.03). Additionally, the percentage of false positives diagnoses was lower in heifers that ovulated to the 1st TAI protocol (P = 0.001). In conclusion, for resynchronization 14 days after TAI, it is not necessary to inject P4i at the beginning of the protocol. In addition, P4 device removal after 6 instead of 8 days increases the percentage of false positives because of the earlier diagnosis (20 days after TAI), but does not interfere in P/AI of resynchronization protocol. Furthermore, the percentage of false positives is higher in heifers that did not ovulate to 1st TAI protocol.

Effects of eCG and FSH in timed artificial insemination treatment regimens on estrous expression and pregnancy rates in primiparous and multiparous Bos indicus cows.

Effects were evaluated in Bos indicus cows of eCG and FSH on follicular growth, estrous expression, and pregnancy per artificial insemination (P/AI) as a result of fixed-time artificial insemination (TAI). In Experiment 1, extent of timing-of-ovulation synchronization among cows was evaluated after imposing an estrogen/progesterone-based treatment regimen. At progesterone device removal (D8), cows were administered: eCG, or FSH or served as untreated Controls. In Experiment 2, percentage of cows P/AI was evaluated when the Experiment 1-treatment regimen was imposed. On D10, all cows were artificially inseminated. In Experiment 3, cows were assigned to two treatment groups (Control and eCG) on D8 to evaluate percentage of cows P/AI and estrous expression. In Experiment 1, follicular dynamics were similar among treatment groups. In Experiment 2, follicular growth was greater (P = 0.0001) with the eCG treatment. There was an interaction of treatment × parity (P = 0.007) on percentage of cows P/AI. There was a greater percentage of primiparous cows P/AI in the eCG-treated than Control and FSH-treated cows. There was a greater percentage of eCG-treated multiparous cows pregnant as a result of TAI than Control cows. There was an interaction of treatment × parity (P = 0.005) on P/AI in Experiment 3, in which the eCG effect was more pronounced in primiparous cows. Treatment with FSH, therefore, was not as effective as eCG in stimulation of follicular growth or enhancing percentage of cows pregnant as a result of TAI. Physiological effects of eCG, however, were also more evident in primiparous cows.

Presynchronization by induction of a largest follicle using a progesterone device in GnRH-based-ovulation synchronization protocol in crossbred dairy cows.

The objective was to compare the fertility of dairy cows using a presynchronization protocol by induction of a largest follicle using a progesterone intravaginal device prior to an Ovsynch protocol (P4synch) with the Double-Ovsynch in lactating dairy cows. Lactating Bos indicus x Bos taurus crossbred cows (n = 440) were randomly allocated to one of two treatments: (I) Double-Ov (n = 228), GnRH (D-17), PGF2α 7 days later (D-10) and GnRH 3 days later (D-7) followed by an Ovsynch protocol 7 days later (GnRH on D0, PGF on D7, GnRH on D9); (II) P4synch (n = 212), insertion of a sustained release progesterone intravaginal device (D-10), 10 days later (D0) an Ovsynch protocol was initiated (GnRH on D0, PGF on D7, GnRH on D9) with progesterone device withdrawal on Day 7. All cows were artificially inseminated (TAI) 16 h after the second GnRH of the Ovsynch protocol and pregnancy diagnosis was performed by transrectal ultrasonography 30 and 60 days after TAI. A subset of cows (n = 52 for Double-Ov and n = 50 for P4synch) ultrasonography was performed on days 0, 7, 9 and 24 of the experimental period. There were no differences among treatments on presynchronization rate [presence of a follicle>12 mm on D0, Double-Ov 94.2% (49/52) and P4synch 92.0% (46/50); P = 0.66], follicular diameter on the 1st GnRH (Double-Ov 17.2 ±â€¯0.7 mm e P4synch 18.6 ±â€¯0.9 mm; P = 0.28), ovulation rate to the 1st GnRH [Double-Ov 86.3% (44/51) and P4synch 81.2% (39/48); P = 0.50], synchronization rate [presence of a follicle>12 mm on D9; Double-Ov 84.6% (44/52) and P4synch 86.0% (43/50); P = 0.84], follicular diameter on the 2nd GnRH (Double-Ov 17.5 ±â€¯0.6 mm and P4synch 18.0 ±â€¯0.5 mm; P = 0.48), ovulation rate to the 2nd GnRH [Double-Ov 90.9% (40/44) and P4synch 86.0% (37/43); P = 0.48] and CL diameter on D24 (Double-Ov 27.9 ±â€¯0.7 mm and P4synch 29.4 ±â€¯0.9 mm; P = 0.19). Corpus luteum presence on D0 was different (P = 0.03) among treatments [Double-Ov 57.7% (30/52) and P4synch 36.0% (18/50)]. There was no difference (P = 0.85) among the pregnancy per AI on day 30 [Double-Ov 39.0% (89/228) and P4synch 40.1% (85/212)], on day 60 [Double-Ov 34.8% (79/227) and P4synch 38.7% (82/212); P = 0.41] and pregnancy loss [Double-Ov 10.2% (9/88) and P4synch 3.5% (3/85); P = 0.08]. The presynchronization by induction of a largest follicle using a sustained release progesterone device prior to Ovsynch yielded similar results compared with the Double Ovsynch protocol on follicular development patterns and on the fertility of lactating dairy cows.

Molecular and endocrine factors involved in future dominant follicle dynamics during the induction of luteolysis in Bos indicus cows.

The growth profiles of the future dominant follicle (DF) and subordinate follicle (SF) and the gene expression of the granulosa cells during luteolysis induction in Bos indicus cows were evaluated. Forty cows were synchronized with a progesterone and estradiol based protocol. After synchronization, cows with a corpus luteum (CL) were evaluated by ultrasonography every 12 h, beginning at eight days post ovulation. Cows identified with a follicle of at least 6.0 mm in diameter in the second wave were split into two groups (BD-before follicular deviation and AD-after follicular deviation. In the BD group cows received 500 µg of cloprostenol (a synthetic analogue of prostaglandin F2α) when the DF reached a mean diameter of 7.0 mm (6.5-7.5 mm). In the AD group, cows received 500 µg of cloprostenol when the DF reached a mean diameter of 8.0 mm (7.5-8.5 mm). Cows in both groups were submitted to aspiration of the DF at 96 and 72 h after prostaglandin was given. Follicular aspirations were performed to quantify IGF1R, LHR and PAPPA transcripts in the granulosa cells. The diameter of the DF at the moment of prostaglandin administration (P = 0.001) and the growth rate of the SF (P = 0.05) were greater in the AD group. There was greater abundance of LHR transcripts in BD cows (P = 0.04). The remaining variables tested were similar between the experimental groups (P > 0.05). In conclusion, the induction of luteolysis before follicular deviation does not interfere with dominant follicle dynamics. However, it causes granulosa cell LHR down regulation.

Effects of eCG are more pronounced in primiparous than multiparous Bos indicus cows submitted to a timed artificial insemination protocol.

The effects of eCG on follicular growth, ovulation, and pregnancy per artificial insemination (P/AI) in multiparous and primiparous Bos indicus beef cows submitted to timed artificial insemination (TAI) were evaluated in three experiments. In experiments 1 (follicular responses; n = 64), 2 (follicular growth and ovulation rate; n = 662), and 3 (P/AI; n = 2092), cows submitted to TAI were assigned to receive one of two treatments on Day 8 of the synchronization protocol: control (no additional treatment) or eCG (300-IU of eCG intramuscularly). In experiment 1, largest follicle (LF) diameter on Day 8 (P = 0.56) and the interval from progesterone (P4)-device removal to ovulation (P = 0.79) did not differ between treatments. However, the maximum diameter of the LF (P = 0.05) and ovulation rate (P = 0.03) were greater in cows that received eCG. In experiment 2, the diameter of the LF on Day 10, follicular growth, and ovulation rate were greater in eCG-treated cows (P < 0.01). However, CL diameter was similar between treatments (P = 0.11). In experiment 3, there was a treatment-by-parity interaction (P = 0.003) on P/AI, such that treatment with eCG was more effective in primiparous cows. In conclusion, eCG treatment resulted in increased final follicular growth, ovulation rate, and fertility in B indicus cows submitted to TAI protocols, especially in primiparous cows.